1. Field of the Invention
This invention pertains to colorable chromogenic compounds eligible for use in pressure-sensitive record material. Pressure-sensitive mark-forming record systems, single sheet and manifold, are improved by use of these compounds.
More specifically, this invention relates to chromogenic compounds having two vinyl linkages which compounds have the form of substantially colorless or slightly colored solids, or which approach being colorless when in liquid solution; but, which may be converted to dark-colored forms upon reactive contact with acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by effecting localized reactive contact between the chromogenic material and the acidic material on or in such web or sheet, such material being brought thereto by transfer or originally there, in situ;--the desired reactive contact forming dark-colored materials in the intended image-marking areas.
The chromogenic compounds of this invention have the following general formula: ##STR3## wherein A and B can be ##STR4## X, Y, and Z can be, among several others, hydrogen, alkyl, alkoxy, aryl, and heterocyclic, substituted and unsubstituted; and E can be a broad family of aromatic and heterocyclic structures.
The chromogenic compounds of this invention especially relate to marks at or near the near infrared part of the color spectrum; and, in that regard, especially relate to providing a color which is particularly visible to machine readers and copiers.
2. Description of the Prior Art
Several phthalide and fluoran chromogenic compounds have been disclosed. For example, U.S. Pat. Nos. 3,491,111, and 3,491,116, issued Jan. 20, 1970, disclose indol- and carbazol-substituted phthalides. U.S. Pat. No. 2,417,897, issued Mar. 25, 1947, discloses crystal violet lactone. U.S. Pat. No. 3,681,390 issued Aug. 1, 1972, discloses arylsubstituted fluorans.
U.S. Pat. No. 3,672,935, issued June 27, 1972, discloses use of colorless chromogenic compounds in pressure-sensitive record material.
G. Hallas, in the Journal of the Society of Dyers and Colourists, in September, 1967 at pages 368 to 373 and in June, 1970 at pages 237-242 discusses the effects of extended conjugation on colored dye compounds.